1. Field of the Invention
The present invention relates to a cover lay film having an electromagnetic wave shielding function and a flexible printed wiring board including the same.
Priority is claimed on Japanese Patent Application No. 2012-222118, filed Oct. 4, 2012, the entire content of which is incorporated herein by reference.
2. Description of Related Art
Since an electromagnetic wave noise generated from a flexible printed wiring board, electronic parts or the like may affect other electric circuits or electronic parts and cause a malfunction thereof or the like, it is necessary to shield the electromagnetic wave noise. Therefore, electronic devices or flexible printed wiring boards have been given a wave shielding function.
Further, with the miniaturization and multifunctionalization of electronic devices including a flexible printed wiring board, a space allowed for the flexible printed wiring board becomes smaller. Therefore, thinning and a reduced bending radius are required for the flexible printed wiring board, and functioning without breaking wiring conductors under a severe bending condition is required.
For example, the following flexible printed wiring boards are proposed as flexible printed wiring boards with an electromagnetic wave shielding function.
(1) A flexible printed wiring board in which an undercoat layer, a shielding layer to which a conductive paste containing a metal powder is applied, and an overcoat layer are sequentially provided on a copper foil wiring circuit which is provided on a heat-resistant plastic film surface. A ground pattern of the copper foil wiring circuit and the shielding layer are electrically connected at an appropriate interval by penetrating through the undercoat layer (Japanese Patent Laid-Open Publication No. H2-33999)
(2) A flexible printed wiring board in which an electromagnetic wave shield film including a metal thin film layer and a conductive adhesive layer with a metal filler sequentially provided on one surface of a cover lay film is placed on a base film with an insulating layer insulating a printed circuit except for a part of a ground circuit such that the conductive adhesive layer is adhered to the insulating layer and the part of the ground circuit (Japanese Patent Laid-Open Publication No. 2000-269632)
(3) A flexible printed wiring board with a cover lay film in which an electromagnetic wave shielding layer is provided on one surface of the cover lay film, a resistor layer having a greater area than the electromagnetic wave shielding layer is provided on the other surface, and an electromagnetic wave noise flowing as a high-frequency current in the electromagnetic wave shielding layer flows as an overcurrent from an edge portion of the electromagnetic wave shielding layer to the resistor layer to be heat-dissipated in the resistor layer (Japanese Patent Laid-Open Publication No. 2009-283901).